Donald J. Trump plans to throw Bill Clinton’s infidelities in Hillary Clinton’s face on live television during the presidential debates this fall, questioning whether she enabled his behavior and sought to discredit the women involved.

And he intends to portray Mrs. Clinton as fundamentally corrupt, invoking everything from her cattle futures trades in the late 1970s to the federal investigation into her email practices as secretary of state.

Drawing on psychological warfare tactics that Mr. Trump used to defeat “Lyin’ Ted” Cruz, “Little Marco” Rubio and “Low-Energy” Jeb Bush in the Republican primaries, the Trump campaign is mapping out character attacks on the Clintons to try to increase their negative poll ratings and bait them into making political mistakes, according to interviews with Mr. Trump and his advisers.

Another goal is to win over skeptical Republicans, since nothing unites the party quite like castigating the Clintons. Attacking them could also deflect attention from Mr. Trump’s vulnerabilities, such as his treatment of women, some Trump allies say.

For Mrs. Clinton, the coming battle is something of a paradox. She has decades of experience and qualifications, but it may not be merit that wins her the presidency — it may be how she handles the humiliations inflicted by Mr. Trump.

She would make history as the first woman to be a major-party nominee, yet she would also be viewed, in part, through the prism of her husband’s flaws. Some political allies and friends, while disgusted with Mr. Trump, see a certain cosmic symmetry at work: After decades of fighting what she once called “the politics of personal destruction,” Mrs. Clinton will reach the White House only if she survives one more crucible of sordid and scandalous accusations.

“She is so prepared to be president, but holding her head high and staying dignified during the campaign is probably what will help her the most,” said Melanne Verveer, a longtime friend and former chief of staff to Mrs. Clinton. “Trump is yet another way she will be tested personally — one of her greatest tests yet.”

Mrs. Clinton has often flourished in the wake of boorish behavior: her husband’s affair with Monica Lewinsky, Kenneth W. Starr’s investigation of her husband, the congressional impeachment proceedings. Women rallied to her side during her 2000 Senate race after her Republican opponent, Representative Rick A. Lazio, invaded her personal space during one debate, and they helped her win the 2008 New Hampshire primary shortly after Barack Obama dismissively said she was “likable enough.”

In a telephone interview, he noted that women did not like seeing Mrs. Clinton insulted or bullied by men. He said he wanted to be more strategic, by calling into question Mrs. Clinton’s judgment in her reaction to Mr. Clinton’s affairs — people close to the couple have said she was involved in efforts to discredit the women — and in her response to crises like Benghazi.

“Just getting nasty with Hillary won’t work,” Mr. Trump said.“You really have to get people to look hard at her character, and to get women to ask themselves if Hillary is truly sincere and authentic. Because she has been really ugly in trying to destroy Bill’s mistresses, and she is pandering to women so obviously when she is only interested in getting power.”

He acknowledged that Republicans tried to discredit her judgment in the marathon Benghazi hearing in the fall, to little avail. But he said that he would be more pointed and memorable in linking her to the failings and deaths in Libya, and that the debate would have a vastly larger television audience than the hearing. Still, advisers of Mrs. Clinton pointed to her face-off with the Republican-led Benghazi committee as a sign of her unflappability.

“From Rick Lazio to the House Benghazi committee, there’s a long line of Republicans who set out to personally attack Hillary Clinton but ended up inflicting the damage on themselves,” a Clinton campaign spokesman, Brian Fallon, said in a statement. “We know Donald Trump is the most unconventional of them all, but no matter what he throws at her, she will keep running her own campaign and won’t hesitate to call him out.”

Several Clinton advisers said they were not underestimating Mr. Trump’s ability to do some damage, acknowledging that Mrs. Clinton’s unfavorability ratings were high — though not as high as Mr. Trump’s — and that many Americans had concerns about her honesty and trustworthiness, according to polls.

But these Clinton advisers expressed confidence that Mr. Trump would overreach and engender sympathy for Mrs. Clinton. Two advisers said that the campaign had done polling to test the possible effectiveness of Mr. Trump’s lines of attacks and, while not disclosing details about the data, that they were convinced that he would not seriously hurt her.

Mrs. Clinton, in turn, has begun attacking Mr. Trump over his refusal to release his tax returns, suggesting he has something to hide, and over his temperament and leadership abilities by describing him as a “loose cannon.” And political allies say that, in time, voters will see through Mr. Trump’s criticisms.

“He can’t run on his forward-looking agenda because he doesn’t have one, and he can’t go after her on substantive policy because she knows so much more than he does,” said Thomas R. Nides, Mrs. Clinton’s former deputy secretary of state for management and resources.

Yet Mr. Trump has been steadily underestimated during the presidential campaign. His Republican rivals were certain that voters would tire of his slashing style and his harsh language, and some political strategists were sure his lack of policy details would make him unprepared in the eyes of too many.

Even one of Mrs. Clinton’s biggest assets to many Democrats — becoming the first female president and returning Mr. Clinton to a White House role — can be exploited as vulnerabilities.

“We’ve never had a woman at the top of the ticket, and there will be plenty of people who’ll have a problem with her gender,” said Christina Greer, a political scientist at Fordham University. And Mr. Trump “can say that Bill Clinton was accused of rape and destroyed a girl’s life who was just a few years younger than his own daughter,” she added, referring to allegations by Juanita Broaddrick of a sexual assault in the 1970s and to the Lewinsky affair.

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With polls showing that Mr. Trump has unprecedented high negative ratings with voters and is in particular trouble with women, some Republican strategists say he has no choice but to try to drive up Mrs. Clinton’s unfavorability ratings. A recent CNN/ORC poll found that 57 percent of likely Trump supporters said that their votes were more to express opposition to Mrs. Clinton than to support Mr. Trump.

“His best way to rally hostile Republican delegates before the convention is to show he’s a great Clinton attack dog,” said Mike Murphy, a Republican strategist who oversaw a “super PAC” supporting Jeb Bush in this year’s Republican race.

Mark Penn, the chief strategist for Mrs. Clinton’s 2008 presidential campaign, and the Harvard University Center for American Political Studies have conducted polling that indicates that attacks against Mrs. Clinton over her private email server, the deaths in Benghazi and other issues would weaken her in a matchup against Mr. Trump.

“The poll shows he could bring her vote down with sharp attacks, but that does not bring his vote up,” Mr. Penn wrote in an email.

At a campaign rally for Mrs. Clinton on Wednesday in New Jersey, some supporters said they were concerned about the damage Mr. Trump could do. They described him as a street fighter and worried that Mrs. Clinton would not be gutsy and nimble enough to deliver a knockout punch.

“Trump is a real lowbrow brawler,” said Michael Magazzu, an entrepreneur in the energy sector from Vineland, N.J. “That’s not her style. She has to counteract him, and the best way may be to keep her cool.”